Refactor AFT backend

* New AFT DB schema - once all experimental stuff is gone, AFT data is really simple
* Build solid feedback model for easier controller implementation
* Remove & refactor lots and lots of pointless and/or abandonned code
* Moved actions-related code into activity class
* Removed "legacyCorrection" method that no longer applies

PS9: Spage's feedback
PS10: Lwelling's feedback
PS13: added unittests
PS15: Spage's feedback
PS18: Spage & Siebrand's feedback
PS21: Spage's feedback
PS23: Spage's feedback

Change-Id: Iebd886f35baf1f593975342c3c96df5233878e44
Merge "Refactor AFT backend"